The main objectives are to test and optimize the in-vitro dynamic tension behavior of two surfactant systems that were discovered to have very low dynamic tensions (less than 5 mN/m) under dynamic area compressions. One is based on a solution of a single soap molecule. The other is a shorter-chain lecithin forming a dispersion of liposomes or vesicles. These systems have the potential to be used as lung surfactant replacement formulations which are simpler and less expensive than current formulations (Survanta and Exosurf) which contain solid particles or complex mixtures derived from animal sources. These systems are also examined for comparison purposes. Using direct probing of the composition of the surface layer and quantitative modeling of the adsorption/desorption behavior will enable some prediction of the effects of dilution or interactions with other surface active components at the alveolar lining layer. Success of this project will lead to better understanding of the mechanisms of operation of the two currently used drugs and may lead to new methods of searching for workable formulations for the neonatal and possibly the adult respiratory distress syndrome.